Printing machine construction

Claim 1

In a printing machine, a combination comprising a first printing roller for printing on one side of a sheet; a second printing roller for printing on the opposite side of said sheet; and means for transferring said sheet from said first to said second printing roller, comprising a transfer roller intermediate said first and second printing rollers and forming with said first printing roller a tangent point, hollow suction bar means on said transfer roller extending over the axial length thereof and operative for engaging a trailing edge of said sheet by suction over the entire elongation of said trailing edge in the direction of said axial length of said transfer roller and for lifting said trailing edge off said first printing roller as said trailing edge travels through said tangent point, means mounting said suction bar means for movement between a position adjacent the periphery of said transfer roller and a position inwardly of said periphery, and combined suction-and-mechanical gripper system means for taking over said trailing edge from said suction bar means and having a row of individual suction grippers for receiving said trailing edge and moving it away from said suction bar means and a plurality of individual mechanical grippers adapted to engage and take over said trailing edge from said suction grippers only after said trailing edge has been received away from said suction bar means by said switch grippers so as to avoid interference between the latter and said mechanical grippers, whereupon said mechanical grippers present said trailing edge to said second printing roller so that it becomes the leading edge when said sheet is on said second printing roller.